Analyzer for gaseous mixtures



s. s. PRENTISS 2,782,103 ANALYZER FOR GASEOUS MfXTURES Filed Oct. 12,1951 Feb. 19, 1957 FIG. 3

FIG. 4

INVENTOR.

S. S. PRENTISS BY HUM qr A TTOR/VE VS United States Patent-O ANALYZERFOR GASEOUS MIXTURES Spencer S. Prentiss, Bartlesville, kla., asslgnorto Phillips Petroleum Company, 'a corporation of Delaware ApplicationOctober 12, 1951, Serial No. 251,115 1 Claim. (Cl. 23-455 such as inmines and around petroleum and chemical processing plants, for example.Efiiciency studies of internal combustion engines, jet engines, and thelike often require an analysis of the exhaust gases therefrom or of thefuel-air ratio of the input feed mixture. In pe troleum exploration anddrilling operations it is desirable to analyze soil and mud particles,since the detection of changes in the combustible gas contained thereinoften gives valuable information as to oil bearing strata. From theforegoing illustrations, which obviously include only a few of the manyapplications of combustible gaseous mixture analysis, it should beapparent that there is a widespread need for eflicient analyzers.

For some time it has been known quite generally that. certainsubstances, in the presence of a combustible. fluid mixture, have theproperty of promoting combustion along their surfaces which results inthe combustible constituents of the fluid mixture uniting with any airoroxygen which may be present. An example of such a substance is platinumwhich is a catalyst of combustion under certain temperature conditions.When a combustible material is brought together with air or oxygen inthe presence of such a catalyst of combustion, the temperature of thelatter isincreased by an amount depending upon the proportion ofcombustible constituents present. By measuring this increase intemperature there is provided an indication of thepercentage ofcombusti-' bles present in the mixture. In accordance .withjthisprinciple, apparatus has been provided for detecting combustion of agaseous. mixture on the surface: of aheated platinum filament. Heatgenerated by the oxidationxof the gas increases the temperature of thefilament thereby resulting in an increase in the electrical resistanceof said filament. This change in resistance is measured by means of aWheatstone bridge circuit wherein the platinum filament constitutes oneof the resistance arms of said bridge. analysis based upon thiscatalytic property of platinum employs a strip of platinum wirepositioned around the bulb of a thermometer device. Any increase intemperature of the platinum due to combustion taking place on itssurface is indicated by the reading of the thermometer. While thesevarious known devices operate in a satisfactory manner under certainconditions, most of these devices lack the desired degree of portabilityand rigidity which is needed in many testing operations. A furtherlimitation is that these devices usually require that the gaseousmixtures under analysis be-maintained within an analysischamber.

Another known method of gaseous paratus;

It is toward providing an improved form of gaseous analyzer and detectorthat the present invention is directed. In accordance therewith, acatalytic agent 1s disposed upon the surface of a flame detecting dev cewhich can be positioned directly in the region of a mixture underanalysis. The improved form of flame detecting device employed in thismanner is essentially of the form described in the copending applicationof D. R. De Boisblanc, Serial No. 220,113, filed April 9, 1951, entitledDetecting Device.

Accordingly, an object of this invention is to provide.

means for safely and accurately indicating the presence of an explosiveor gaseous mixture.

Another object is to provide means for analyzing gaseous mixtures todetermine the proportions of combustible components present therein.

A further object is to provide means for analyzing the fuel-air ratio offeed streams to internal combustion and other type engines.

- A still further object is to provide apparatus for carrying out theabove-mentioned objects which is simple to construct, easy to operate,and which is capable of giving rapid reliable results.

7 Various other objects, advantages, and features of this inventionshould become apparent from the following detailed description taken inconjunction with the accompanying drawings illustrating a preferredembodiment of this invention in which:

Figure 1 is a schematic view of a combustible gaseous mixture detectingprobe together with suitable electrical indicating circuitry;

' Figure 2 illustrates a second form of the testing ap-' Figure 3 showsa modification of the apparatus of Figure 1 especially adapted to detectthe presence of explosive vapors; and

Figure 4 illustrates an application of this analysis instrument forstudying the fuel-air input mixtures to internal combustion engines. 1

. An improved form of combustion detecting device recently has beendeveloped which relies upon the principle that in any given electricalresistance element having two electrodes connected thereto, one of whichis grounded,

there exists a constant distribution of potential at all.

points throughout said element. If an electrically charged particle isbrought into contact with the surface of this element electrical currentwill flow therein until.

all points within the element are once again at zero or groundpotential.

the ungrounded electrode exhibits a potential variation which isdependent upon the magnitude of the charge of the particles strikingsaid element, the electrical resistance of the element, and thegeometric relation of the ungrounded electrode with respect to thesecond grounded,

propriate apparatus which can be usedin this manner for flame detection.

Referring now to the drawings in detail and to'Figure l in particular,there is shown a combustion detecting element 10 comprising acylindrical metallic casing 11 having a metallic electrode 12 positionedtherein and'electrically insulated from casing 11 by means of suitablein-- sulating support such as 13. A ceramic refractory tip.

Patented Feb. 19, 1957 During the time when current is flowing, theregion of the'element in the neighborhood of 14; into which, Whileplastic, is inserted the hook 'shaped end of electrode 12, is positionedacross one end of casing 12 and anchored thereto by suitable holes 15drilled near the tender casing 11. Tip 14 preferably is cdhst ructe'd ora baked and hardened rerractor' f material seen as aluminum oxide.Electrode 12 is fitted somewhat'lo'osely into casing 10 so as not towork loose from tip 14 due to thermal expansion at elevatedtemperatures. .Upon the surface of refractory tip 14 there is formed apartial coat ing of suitable combustion promoting catalytic materialsuch as, for example, thin strips 16 of platinum or other combustionsupporting materials which are discussed fully hereinafter. Electricalleads 17 and 18 are attached to casing 11 and electrode 12,respectively, to; connect cumbustion detecting element 10 into theassociated electrical circuitry which comprises an alternating currentamplifier 21 and an output indicating device or meter 22.

The operation of the flame detecting probe per se, which" is not thesubject of the present invention, can be ex-. plained in the followingmanner. Assuming that tip 14' is positioned in the region of a flame,then the ions con tained within said flame will bombard the surface oftip I4 and in so doing generate electrical voltage fluctuation acrosssaid tip. Each ion that strikes tip 14 introduces a small burst ofcurrent therein. It is believed that the voltage fluctuations generatedbetween casing 11 and elec node 12 by the individual bursts of currenthave a sta tistical fluctuation in magnitude over .a Wide frequencyrange. However, these electrical signals must be amplified many fold byamplifier 21 before being' of sufficient magnitude to give a readablesignal on meter 22.

The present invention, however, is directed to the ad dition of asuitable combustion supporting catalyst such as platinum strips 16 totip 14. When probe 10 is inserted into the region of a combustiblemixture there iswith amplifier 21 by means of connecting leads 27 and28, respectively. The output of amplifier 21 is indicated on meter 22.Partial coatings 29 and 30 of combustion supporting catalytic materialare formed on the opposing surfaces of electrodes 25 and 26,respectively. The operation of this second form of detecting device isessentially the same as that of the probe in Figure 1, it having beenfound that the air gap between electrodes 25 and 26 serves essentiallythe same function as the ceramic noise resistance element 14 positionedbetween casing 11 and electrode 12 in Figure l, and that coatings 29 and30 serve the same function as coating 16 on element 14.

In Figure 3 there is shown a portable combustion detecting unit which isparticularly adapted to determine the existence of an explosive mixturesuch as may be encountered in mines, for example. Probe unit 10 containsan elongated casing 11 which can serve as a handle for convenientlycarrying the probe unit into a region containing what may be anexplosive atmosphere. Tip portion 14, upon which combustion readilytakes place due to platinum coating 16 thereon, is completely enclosedwithin a screen of an effective heat conducting material such as copperwire. Screen 35 serves to prevent any flame which may be initiated uponthe surface of tip 14 from escaping outward therefrom, said screen 35forming essentially a Davys safety lamp. Probe 10 is connected by meansof a flexible conduit 36 to a portable indicating unit 37 which containsamplifier 21 and output meter 22. In place of, or in addition to, outputmeter 22, a suitable warning device such as a bell or buzzer can Thissur- In this manner the air input mixture through intake manifold 41.Inserted within manifold 41 is a probe element 10 surrounded by aprotecting wire screen 35. Electrode 12 is connected to the input ofamplifier .21 by an electrical lead 42, the input circuit beingcompleted by a grounded lead which portion thereof.

can be applied directly to a manifold 41. The input fuel-air mixturewhich enters engine thus surrounds probe 10 which is employed toinitiate combustion of a Protective screen 35 preventsthis combustionfrom taking place throughout manifold '41. Since the reading on outputmeter 22 is indicative of the degree of combustion taking place uponprobe 10, this meter reading can becalibrat'ed to give an indication ofthe prope'r fuel-air mixture enteringengine 40. This is true hecause thedegree of combustion is influenced by the ratio of fuel to air suppliedengine 40. In addition to its use asanindicating device, the outputsignal of amplifier 21 can be applied to suitable control mechanism toregulate the fuel-air input' supplied by the carburetor, not shown; Inthis manner engine 40 can be operated at the condition of maximumefficiency by proper regulation of its fuelair input ratio.Approximately the same results can be obtained by positioning thecombustion detecting probe 10" within theexhaust fumes of engine 40. Bymeasuring the cbmbnstible' content of the output exhaust fumes, a

, various other materials can be employed as combustion supportingcatalytic agents;

It has been found that even the stablest organic substances when mixedwith air and passed over suitable catalytic surfaces will commence tooxidize at quite moderate temperatures. Particularly active in thisrespect are the various metals of the platinum group which includeplatinum, palladium, iridium, rhodium, osmium and ruthenium. Inaddition, the oxides of iron, cobalt, nickel, chromium, copper,manganese, silver, and cerium are catlytic in somewhat the same manner.

- Platinum black, platinum sponge and the corresponding forms ofpalladium also are quite active as well as the metallic elementsthemselves. For the detection of carbon monoxide, the catalystI-Iopcalite" is particularly elfective'. Hopcalite is a mixture of thefollowing approximate composition: cupricoxide, 30 percent; manganeseperoxide, 50 percent; cobaltic oxide, 15 percent; and

silver oxide, 5 percent.

The detecting elements of this invention can be constructed in variousmanners; one of which comprises depositing a coating of the catlyticactive material upon a portion of the surface of the probe elementitself. This coating can be in the form of thin strips or wires of thecatalytic material disposed either directly on the surface of the probeor protruding therefrom like whiskers. A

' second mode of construction comprises mixing a quantity of thecatalytic material with the material of which the probe tip is formed,the latter procedure resulting in catalytic points being formed on thesurface of the probe whichserves toisolate the combustion at saidindividual has a greater safety factor when used in the detection ofexplosive vapors.

In constructing the probe element of Figure 1 various ceramic refractorymaterials can be used in addition to aluminum oxide to form the tipelement 14. Examples of these substances which have been found effectiveinclude the oxides of calcium, magnesium, zirconium, beryllium, andthorium; and the carbides of titanium, zirconium, columbium, tantalum,silicon, tungsten, and hafnium. The probe element itself can beconstructed in various configurations as illustrated in the copendingapplication of R. S. Marsden, Jr., Serial No. 220,116, filed April 9,1951, entitled Electrical Noise Element. As therein illustrated casing11 can be formed of a ceramic material as can electrode 12; in additiontwo electrodes can be positioned within casing 11 thereby eliminatingcasing 11 as one of the output electrodes. A still further examplecomprises a mass of ceramic material having two metallic electrodespositioned therein.

Amplifier 21 can be any conventional alternating current amplifieradapted to pass a wide band of frequencies. Since the detected noisesignals are of relatively small amplitude amplifier 21 must have highgain and should have little electrical noise introduced therein in orderthat a maximum signal can be transmitted thereby. The output ofamplifier 21 can be indicated on any suitable metering device such as athermocouple voltmeter or can be rectified to actuate any direct currentcontrol or recording mechanism.

While this invention has been described in conjunction with presentpreferred embodiments thereof, it should be apparent that variouschanges in details of the apparatus can be made without departing fromthe scope of the invention; and, further, that the theory set forth,although believed to be accurate, is not considered as the sole basis ofthe operativeness of this invention. This apparatus does operatesuccessfully and effectively whether or not upon the principlesdescribed herein.

Having described my invention, I claim:

Apparatus for indicating the presence of a combustible gaseous mixturecomprising a metallic casing having an electrode positioned within andelectrically insulated from the casing, a tip of electrically conductiverefractory material positioned between and electrically connecting saidcasing and said electrode, a catalytically active agent positioned onsaid tip, said agent being capable of initiating combustion of a gaseousmixture to be analyzed, alternating current amplifying means having theinput terminals thereof connected to said electrode and said casing,respectively, and means to indicate the output signal of said amplifyingmeans which is representative of electrical voltage fluctuations thatare generated by combustion of the mixture to be analyzed taking placein the region of said tip.

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